Hydrogen recovery from hydrocarbon synthesis processes

ABSTRACT

The invention relates to a process for producing a hydrogen-rich stream from a hydrogen-depleted stream. More particularly, the invention relates to a hydrocarbon synthesis process, by way of example, a Fischer Tropsch process, from which both hydrocarbons and high purity hydrogen are obtained. The process comprises contacting the hydrogen-depleted stream with a reverse-selective membrane to provide a CO 2 -enriched permeate and a hydrogen-containing retentate. The high purity hydrogen is produced from the hydrogen-containing retentate. The high purity hydrogen thus obtained may be used in a process selected from the group consisting of upgrading hydrocarbons produced from the hydrocarbon synthesis process, hydrotreating a natural gas stream, recycling to the hydrocarbon synthesis reaction unit, high purity hydrogen production, catalyst rejuvenation, and combinations thereof.

RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.10/794,084, filed Mar. 8, 2004, now U.S. Pat. No. 7,166,643 the contentsof which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to a process for producing a hydrogen-rich streamfrom streams comprising a low concentration of hydrogen, i.e., ahydrogen-depleted stream. More particularly, the invention relates to ahydrocarbon synthesis process, by way of example, a Fischer Tropschprocess, from which both hydrocarbons and high purity hydrogen areproduced.

BACKGROUND OF THE INVENTION

There are many processes known in the art for converting hydrocarbonsources such as natural gas, coal, coke, into more valuable hydrocarbonproducts. A typical conversion process involves first converting thehydrocarbon source into synthesis or syngas gas, which is a mixture ofwater, carbon dioxide, carbon monoxide and hydrogen. If the hydrocarbonsource is natural gas, a catalytic reforming reaction is utilized tomake syngas. If the source is residual oil or a solid feed, partialoxidation or gasification is used. The syngas then may be used as afeedstock for producing a wide range of chemicals, including combustibleliquid fuels, methanol, ammonia, acetic acid, dimethyl ether, oxoalcohols, and isocyanates.

Remote natural gas assets can be converted into conventionaltransportation fuels, chemical feedstocks, and lubricants via theinitial production of syngas. The Fischer Tropsch process is theconventional route to convert the syngas into transportation fuels andlubricants. Alternatively, natural gas may be converted into syngasfollowed by methanol synthesis with the methanol utilized to produce awide variety of chemicals.

In particular, a Fischer Tropsch synthesis reaction may be used tosynthesize higher molecular weight hydrocarbon products from synthesisgas. In Fischer Tropsch synthesis reactions, synthesis gas is convertedto hydrocarbons by contact with a Fischer Tropsch catalyst underreactive conditions. The products from a Fischer Tropsch process mayrange from C₁ to C₂₀₀₊ with a majority in the C₅-C₁₀₀₊ range. TheFischer Tropsch synthesis reaction can be conducted in a variety ofreactor types including, for example, fixed bed reactors containing oneor more catalyst beds, slurry reactors, fluidized bed reactors, or acombination of different type reactors.

Similarly, methanol can be produced from a wide range of hydrocarbonfeedstocks by initially converting the feedstock into synthesis gas byreforming or gasification. Methanol synthesis can then be achieved via acatalytically-enhanced reaction.

Hydrocarbon synthesis processes typically require a source of hydrogengas for use in the process. By way of example, natural gas feeds to thesynthesis gas generator may require hydrotreating prior to introductioninto the synthesis gas generator. In addition, Fischer Tropsch products,while they are highly paraffinic, are typically upgraded by one or morehydroconversion processes to provide more valuable products. Examples ofhydroconversion processes include hydrotreating, hydrocracking,hydroisomerization, and hydrofinishing. In thesehydroconversion/hydrotreating processes, expensive hydrogen gas isconsumed.

Conventional sources of hydrogen gas are expensive. The hydrogen gas maybe obtained from a conventional steam methane reformer; however, theequipment is expensive and the process requires a natural gas feed,which instead could be used to generate additional syngas and ultimatelymore valuable higher molecular weight products. Hydrocarbon synthesisprocesses generate gas streams comprising low concentrations ofhydrogen. However, the hydrogen is in such low concentrations thattypically, these gas streams are sent to fuel gas systems.

As hydrocarbon synthesis processes require hydrogen gas and typicalsources for hydrogen gas are expensive, there have been attempts todevelop more economical and efficient sources of hydrogen gas for use inthese hydrocarbon synthesis processes. By way of example, U.S. Pat. Nos.6,043,288 and 6,103,773 and WO 02/051744 describe processes forproducing hydrogen from a synthesis gas feed. U.S. Pat. No. 5,082,551describes a process for the separation of H₂-rich gas from the effluentfrom a hydroconversion zone and U.S. Pat. No. 6,147,126 describesprocesses for using the H₂-rich tail gas from a hydroconversion processfor at least one of (i) hydrocarbon synthesis reaction catalystrejuvenation, (ii) the hydrocarbon synthesis, and (iii) hydrogenproduction. U.S. Pat. No. 5,844,005 describes using a hydrogencontaining tail gas from a hydrocarbon synthesis reactor as a hydrogencontaining catalyst rejuvenating gas. If CO is present in the hydrogencontaining tail gas, the CO content is less than 10 mole % of the gasand the H₂ to CO mole ratio is greater than 3:1.

Accordingly, there is a need in the art for an economical and efficientsource of hydrogen gas. As such, there is a need in the art forprocesses for providing high purity hydrogen gas from gas streamscomprising low concentrations of hydrogen. In addition, there is a needin the art for a hydrocarbon synthesis process in which the hydrogenrequired for hydrotreating the natural gas feed and/or upgrading theproducts is economically and efficiently provided from the hydrocarbonsynthesis process itself such that the use of hydrogen from an outsidesource is minimized. This invention provides such processes.

SUMMARY OF THE INVENTION

The present invention relates to a process for providing a hydrogen-richstream. The process comprises performing a hydrocarbon synthesis processusing syngas and isolating a gaseous stream comprising hydrogen from thehydrocarbon synthesis process. The gaseous stream comprising hydrogen iscontacted with a reverse-selective membrane to provide a CO₂-enrichedpermeate and a hydrogen-containing retentate, the retentate is passedthrough a water gas shift reactor to provide a hydrogen-containingstream; and the hydrogen-containing stream is passed through a pressureswing adsorption unit to provide a hydrogen-rich stream comprisinggreater than 90 vol. % hydrogen.

In another embodiment, the present invention relates to a process forproviding a hydrogen-rich stream. The process comprises performing ahydrocarbon synthesis process using syngas and isolating a gaseousstream comprising hydrogen from the hydrocarbon synthesis process. Thegaseous stream comprising hydrogen is passed through a water gas shiftreactor to provide a hydrogen-containing stream; the hydrogen-containingstream is contacted with a reverse-selective membrane to provide aCO₂-enriched permeate and a hydrogen-containing retentate; and thehydrogen-containing retentate is passed through a pressure swingadsorption unit to provide a hydrogen-rich stream comprising greaterthan 90 vol. % hydrogen.

In yet another embodiment, the present invention relates to a processfor providing a hydrogen-rich stream. The process comprises performing ahydrocarbon synthesis process, isolating a hydrogen-depleted stream fromthe hydrocarbon synthesis process, and isolating a hydrogen-rich streamcomprising greater than 90 vol. % hydrogen from the hydrogen-depletedstream by a process comprising contacting the hydrogen-containing streamwith a reverse-selective membrane.

In a further embodiment, the present invention relates to a process forupgrading a hydrocarbon product stream comprising contacting thehydrocarbon product stream with a hydrogen-rich stream, wherein thehydrogen-rich stream is isolated from a stream comprising less than 40%vol. hydrogen.

In yet a further embodiment, the present invention relates to anintegrated Fischer Tropsch process. The process comprises performing aFischer Tropsch process using syngas to provide a hydrocarbon productstream and a hydrogen-depleted stream; isolating a hydrogen-rich streamfrom the hydrogen-depleted stream; and upgrading at least a portion ofthe hydrocarbon product stream by reacting it with at least a portion ofthe hydrogen-rich stream.

In another embodiment, the present invention relates to a process forproviding a hydrogen-rich stream. The process comprises performing ahydrocarbon synthesis process using syngas to provide at least onehydrocarbon stream and a hydrogen-depleted stream. A hydrogen-containingstream is isolated from the hydrogen-depleted stream by a processcomprising contacting with a reverse-selective membrane and performing awater gas shift reaction, wherein the hydrogen concentration on awater-free basis of the hydrogen-containing stream is at least 5 vol. %greater than the hydrogen concentration on a water-free basis of thehydrogen-depleted stream. The hydrogen-containing stream is passedthrough a pressure swing adsorption unit to provide a hydrogen-richstream comprising greater than 90 vol. % hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of one embodiment of the invention.

FIG. 2 provides Table II, which is a stream summary of the content ofthe gas streams from FIG. 1. The stream summary has been generated bycomputer modeling.

FIG. 3 is a schematic flow diagram of a second embodiment of theinvention.

FIG. 4 provides Table III, which is a stream summary of the content ofthe gas streams from FIG. 3. The stream summary has been generated bycomputer modeling.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, processes are provided for isolatinga hydrogen-rich stream. Surprisingly, the processes of the presentinvention allow for the isolation of a hydrogen-rich stream from streamscomprising a low concentration of hydrogen. Preferably, thehydrogen-depleted streams are isolated from a hydrocarbon synthesisprocess. Low concentrations of hydrogen typically prevent the use ofpressure swing adsorption to recover hydrogen-rich streams. To functioneffectively, pressure swing adsorption typically requires a hydrogenfeed with greater than 40 vol. % hydrogen. However, the processes of thepresent invention allow for the isolation of a hydrogen-rich stream froma hydrogen-depleted stream, in particular a stream comprising less than40 vol. % hydrogen, preferably less than 35 vol. % hydrogen.

The processes for isolating a hydrogen-rich stream according to thepresent invention use methods for raising the concentration of hydrogenin the stream. These methods include using a reverse-selective membranethat is selectively permeable to carbon dioxide, and thus, separatescarbon dioxide from the other components of the hydrogen-depleted gasstream.

Preferably, the processes of the present invention are used to isolatehydrogen-rich streams from streams produced in hydrocarbon synthesisprocesses, and the hydrogen-rich streams thus isolated can then be usedin the hydrocarbon synthesis processes, thus providing an integratedprocess.

The hydrogen-rich streams isolated according to the processes of thepresent invention may be used for any purpose for which a high purityhydrogen gas is needed. By way of example, the hydrogen-rich streams canbe used for a process selected from the group consisting of (i)upgrading a hydrocarbon product stream from the hydrocarbon synthesisprocess; (ii) hydrotreating a natural gas stream; (iii) recycling thehydrogen-rich stream to a hydrocarbon synthesis reaction unit; (iv)hydrogen production for uses outside the hydrocarbon synthesis process;(v) rejuvenating a hydrocarbon synthesis reaction catalyst; and (vi)combinations thereof.

Definitions

The following terms will be used throughout the specification and willhave the following meanings unless otherwise indicated.

The hydrocarbon synthesis process refers to a series of process stepsfor the conversion of a hydrocarbon source, such as natural gas, heavyoil, and coal, into more valuable hydrocarbons. The hydrocarbonsynthesis process first comprises converting the hydrocarbon source intosynthesis gas or syngas. The synthesis gas is then converted into morevaluable hydrocarbons by a hydrocarbon synthesis reaction. Thehydrocarbon synthesis process may comprise one or more upgrading stepsto upgrade the hydrocarbons into one or more salable hydrocarbonaceousproducts. Hydrocarbon synthesis processes may be used to produce a widerange of products, including combustible liquid fuels, methanol, aceticacid, dimethyl ether, oxo alcohols, and isocyanates. Hydrocarbonsynthesis processes include Fischer Tropsch processes, methanolsynthesis processes, and the like.

A hydrocarbon synthesis reaction refers to the reaction that convertssynthesis gas into higher hydrocarbons. Hydrocarbon synthesis reactionsinclude Fischer Tropsch synthesis reactions, methanol synthesisreactions, and the like.

Derived from a Fischer Tropsch process means that the feedstock, feed,product stream, or tail gas in question originates from or is producedat some stage by a Fischer Tropsch process.

A “Fischer Tropsch derived stream” or “Fischer Tropsch stream” meansthat the stream originates from or is produced at some stage by aFischer Tropsch process.

Highly paraffinic means that the feedstock, blend stock, or product inquestion contains more than 70 weight % paraffins, preferably 80 weight% or greater paraffins, and most preferably 90 weight % or greaterparaffins.

Syngas or synthesis gas is a mixture that includes both hydrogen andcarbon monoxide. In addition to these species, water, carbon dioxide,unconverted light hydrocarbon feedstock and various impurities may alsobe present.

Permeate means the gas stream that selectively passes through themembrane. As such, the membrane is selectively permeable for thepermeate.

Retentate means the gas stream that does not pass through the membraneand thus, remains on the feed side of the membrane. As such, themembrane is not selectively permeable for the retentate.

Reverse-selective membrane is a membrane that is selectively permeableto a more soluble gas component. According to the present invention, thereverse-selective membrane is selectively permeable to CO₂ and thus, themembrane selectively passes CO₂ while restricting passage of lesssoluble components in the original feed stream, including hydrogen.

CO₂-enriched permeate means the gas stream that passes through thereverse-selective membrane. The reverse-selective membrane isselectively permeable to CO₂, and as such, the membrane selectivelypasses CO₂ resulting in a gas stream that is enriched in CO₂ anddepleted in the less soluble components of the original gas feed. Itshould be noted that the membrane is selectively permeable to CO₂.Selectively permeable indicates a higher selectivity for CO₂ incomparison to the less soluble components of the original gas feed;however, selectively permeable does not require a complete separation ofthe components of the original gas feed.

Hydrogen-containing retentate means the gas stream that does not passthrough the membrane. The reverse-selective membrane is selectivelypermeable to CO₂, and as such, the membrane restricts passage of theless soluble gas components in the original feed, including hydrogen,resulting in a hydrogen-containing retentate. The hydrogen-containingretentate comprises hydrogen, as well as other components of theoriginal gas for which the membrane is not selectively permeable. Themembrane according to the present invention is selectively permeable toCO₂, and thus, the gas stream, which does not pass through the membrane,comprises hydrogen, as well as other components of the original gas forwhich the membrane is not selectively permeable. Selectively permeableindicates a higher selectivity for CO₂ in comparison to the less solublecomponents of the original gas feed; however, selectively permeable doesnot require a complete separation of the components of the original gasfeed, and thus, the hydrogen-containing retentate may comprise residualCO₂ as well as hydrogen and the other components of the original gas forwhich the membrane is not selectively permeable.

Hydrogen-rich stream means a stream comprising greater than 90 vol. %hydrogen, preferably greater than 95 vol. % hydrogen, and morepreferably greater than 99 vol. % hydrogen.

Hydrogen-depleted stream means a stream comprising less than 40 vol. %hydrogen, preferably less than 35 vol. % hydrogen, and more preferablyless than 30 vol. % hydrogen.

Low value hydrogen streams are hydrogen-depleted streams and thuscomprise less than 40 vol. % hydrogen, preferably less than 35 vol. %hydrogen, and more preferably less than 30 vol. % hydrogen.

Integrated Process means a process comprising a sequence of steps, someof which may be parallel to other steps in the process, but which areinterrelated or somehow dependent upon either earlier or later steps inthe total process. Thus, a feed to one step in an integrated processcomprises a product from a preceding step in the process; alternatively,a product of a step in an integrated process is a feed, either alone oras a blend with other feeds, for one or more subsequent steps in anintegrated process.

“Hydrocarbon or hydrocarbonaceous” means a compound or substance thatcontains hydrogen and carbon atoms, which may also include heteroatomssuch as oxygen, sulfur or nitrogen.

All percentages herein are by volume unless otherwise stated.

The present invention provides processes for isolating a hydrogen-richstream from a hydrogen-depleted stream. As provided above, thehydrogen-rich stream comprises greater than 90 vol. % hydrogen,preferably greater than 95 vol. % hydrogen, and more preferably greaterthan 99 vol. % hydrogen, and the hydrogen-depleted stream comprises lessthan 40 vol. % hydrogen, preferably less than 35 vol. % hydrogen. Theprocesses of the present invention for isolating a hydrogen-rich streamuse a reverse-selective membrane. According to the present invention, aninitial gas stream (i.e., a hydrogen-depleted stream) is treated by aprocess comprising contacting the initial gas stream with areverse-selective membrane.

In one embodiment, the processes for isolating a hydrogen-containingstream from a hydrogen-depleted stream comprise contacting with areverse-selective membrane, performing a water gas shift reaction, andpassing through a pressure swing adsorption unit. Contacting with areverse-selective membrane and performing a water gas shift reaction areperformed prior to passing through a pressure swing adsorption unit toraise hydrogen concentrations to acceptable levels for use of pressureswing adsorption for hydrogen recovery. The processes may furthercomprise removing water in a vapor-liquid separator prior to thepressure swing adsorption unit.

In an embodiment, the processes comprise contacting the initial gasstream with a reverse-selective membrane to provide a CO₂-enrichedpermeate and a hydrogen-containing retentate; passing the retentatethrough a water gas shift reactor to provide a hydrogen-containingstream; and passing the hydrogen-containing stream through a pressureswing adsorption unit to provide a hydrogen-rich stream. The process mayfurther comprise passing the hydrogen-containing stream through avapor-liquid separator to remove water prior to the pressure swingadsorption unit. Advantageously, the hydrogen-containing retentate is atelevated pressure since it does not pass through the membrane and thusdoes not require re-pressuring to complete the isolation process.Preferably, the hydrogen-containing retentate is at a pressure of ≧about 100 psig, and more preferably ≧ about 200 psig.

In another embodiment, the processes of the present invention comprisepassing the initial gas stream through a water gas shift reactor toprovide a hydrogen-containing stream; contacting the hydrogen-containingstream with a reverse-selective membrane to provide a CO₂-enrichedpermeate and a hydrogen-containing retentate; and passing thehydrogen-containing retentate through a pressure swing adsorption unitto provide a hydrogen-rich stream. The process may further comprisepassing the hydrogen-containing stream through a vapor-liquid separatorto remove water prior to the reverse-selective membrane. Advantageously,the hydrogen-containing retentate is at elevated pressure since it doesnot pass through the membrane and thus does not require re-pressuring tocomplete the isolation process. Preferably, the hydrogen-containingretentate is at a pressure of ≧ about 100 psig, and more preferably ≧about 200 psig.

Initial Gas Stream

The initial gas stream to the processes of the present inventioncomprises hydrogen. Advantageously, the processes of the presentinvention allow for isolation of a hydrogen-rich stream from initialstreams that comprise a low concentration of hydrogen. As such, theseinitial gas streams are low value, hydrogen-depleted streams comprisingless than 40 vol. % hydrogen, preferably less than 35 vol. % hydrogen,and more preferably less than 30 vol. % hydrogen. The initial gasstreams may also comprise CO₂, CO, H₂O (g), and gaseous C₁-C₅hydrocarbons.

The initial gas stream may be isolated from any source from which ahydrogen-depleted stream may be obtained. Preferably, thehydrogen-depleted stream is isolated from a hydrocarbon synthesisprocess. In a hydrocarbon synthesis process, the hydrogen-depletedstreams may be isolated from one or more processes that together providesuch a low value hydrogen-containing stream. Preferably, thehydrogen-depleted stream is isolated from a source selected from thegroup consisting of (i) a tail gas from a hydrocarbon synthesis reactionunit; (ii) the syngas prior to performing the hydrocarbon synthesisreaction; (iii) a tail gas from an upgrading process; and (iv)combinations thereof. Preferably, at least a portion of thehydrogen-depleted stream is isolated from the tail gas from ahydrocarbon synthesis reaction unit.

As these initial gas streams, i.e., hydrogen-depleted gas streams,comprise less than 40 vol. % hydrogen, there is insufficient hydrogencontent to produce a hydrogen-rich product by pressure swing adsorption.Surprisingly, a hydrogen-rich stream may be produced from these lowvalue, hydrogen-depleted streams by employing methods to effectivelyraise the hydrogen content of the gas feed prior to pressure swingadsorption. These methods include contacting the initial gas feed with areverse-selective membrane that is selectively permeable to carbondioxide and performing a water gas shift reaction. After conductingthese methods, the hydrogen content on a water-free basis of theresulting stream may be at least 5 vol. % greater than the hydrogencontent on a water-free basis of the initial hydrogen-depleted gasstream.

Reverse-Selective Membrane

The reverse-selective membrane, used in the processes of the presentinvention, is selectively permeable to carbon dioxide and relativelyimpermeable to the less soluble components of the original gas feed,including hydrogen and carbon monoxide. Therefore, when the initial gasstream is contacted with the reverse-selective membrane according to theprocesses of the present invention, a CO₂-enriched permeate and ahydrogen-containing retentate are provided. The CO₂-enriched permeatepasses through the membrane and the hydrogen-containing retentateremains on the feed side of the membrane. As described above,advantageously, the hydrogen-containing retentate is at elevatedpressure since it does not pass through the membrane and thus does notrequire re-pressuring to complete the isolation process. Preferably, thehydrogen-containing retentate is at a pressure of ≧ about 100 psig, andmore preferably ≧ about 200 psig.

Reverse-selective membranes are rubbery membranes and they operatebecause bigger, more condensable molecules (i.e., more solublemolecules) are preferentially permeated. Solubility is the key factorthat enables CO₂ to preferentially permeate over the less solublecomponents including H₂.

In contrast, most other typical membranes (i.e., “regularly-selective”membranes) are glassy membranes, and as such, smaller molecules diffusemuch faster through the membrane than larger molecules. Diffusivity,rather than solubility, is the controlling factor for this type ofmembranes. In “regularly-selective” membranes, hydrogen will permeateacross the membrane more readily resulting in a retentate containingCO₂.

Reverse-selective membranes, which are selectively permeable to carbondioxide and are useful in the processes of the present invention, areavailable from Membrane Technology and Research, Inc. in Menlo Park,Calif. Reverse-selective membranes available from Membrane Technologyand Research, which are selectively permeable to carbon dioxide, may bebased on polyether-polyamide block copolymers. The permeation propertiesof these membranes are optimized for separating polar gases fromnonpolar gases.

Membranes that are selectively permeable to carbon dioxide are availablefrom Membrane Technology and Research, Inc. in Menlo Park, Calif. andhave been described in U.S. Pat. Nos. 4,963,165; 6,361,583; 6,572,679;and 6,572,680 (assigned to Membrane Technology and Research), thecontents of which are incorporated by reference in their entirety.Reverse-selective membranes that are selectively permeable to CO₂preferably exhibit selectivities of CO₂/H₂ of up to 10.

The structure of the polyether-polyamide block copolymers of thereverse-selective membrane available from Membrane Technology andResearch is as illustrated below:

wherein PA is an aliphatic polyamide block and PE is a polyether block.As such, there is a repeat unit of polyether-polyamide block copolymers.The aliphatic polyamide (PA) units are those such as nylon 6 or nylon 12and the polyether (PE) units are those such as polyethylene glycol orpolytetramethylene glycol.Water Gas Shift Reactor

Either prior to contact with the reverse-selective membrane or aftersuch contact, the hydrogen-containing stream is passed through a watergas shift reactor. In the water gas shift reactor CO reacts with watervapor in the presence of a shift catalyst at reaction conditionseffective to form a mixture of hydrogen and carbon dioxide. Water gasshift reaction conditions are well known to those of skill in the art.Shift catalysts include, for example, iron-based shift catalysts,copper-based shift catalysts, and nickel-based shift catalysts.

The iron-based catalysts are known as high temperature shift catalysts,and generally operate in the temperature range of 320-450° C. Copperbased catalysts are known as low temperature catalysts, and generallyoperate in the temperature range of 200-250° C. Industrial shiftconverters can operate from atmospheric pressure to 8500 kPa, at COconcentrations between 3% and 80%.

Many other transition metals have been shown to demonstrate some shiftactivity. One which has received attention is the sulfided cobaltoxide-molybdenum oxide on alumina. Other catalysts, including cobaltFischer Tropsch catalysts, are also known to have at least some shiftactivity.

In the processes according to the present invention a gas streamcomprising CO and H₂ is fed into a water gas shift reactor with excesswater vapor to provide a stream with increased hydrogen content.Providing water vapor in excess assists in driving the reaction toformation of hydrogen and carbon dioxide. After the water gas shiftreaction excess water may be removed by cooling and passing the streamthrough a vapor-liquid separator.

Water gas shift reaction conditions are described, for example, inNewsome, David S., “The Water-Gas Shift Reaction,” Catal. Rev.-Sci.Eng., 21 (2) pp 275-318 (1980).

Pressure Swing Adsorption

Contacting with a reverse-selective membrane and performing a water gasshift reaction are performed prior to passing through a pressure swingadsorption unit to raise hydrogen concentrations to acceptable levelsfor use of pressure swing adsorption for hydrogen recovery. To operateeffectively, the hydrogen-containing gas feed to the pressure swingadsorption unit needs to comprise greater than about 40 vol. % hydrogen.The initial gas stream is contacted with a reverse-selective membraneand passed though a water gas shift reactor raising the volume percentof hydrogen on a water-free basis in the gas stream. After conductingthese methods, the hydrogen content on a water-free basis of theresulting stream may be at least 5 vol. % greater than the hydrogencontent on a water-free basis of the initial hydrogen-depleted gasstream. Therefore, surprisingly using the processes of the presentinvention a hydrogen-depleted stream may be used as the initial gasstream for providing a hydrogen-rich stream.

Pressure swing adsorption operates to purify the hydrogen-containing gasby removing contaminant gases and hydrocarbons. The hydrogen-containinggas, which is the feed to the pressure swing adsorption unit comprises,greater than 40 vol. % hydrogen for the unit to operate effectively.Higher concentrations of hydrogen result in higher hydrogen recoveryefficiencies and better economics. Pressure swing adsorption systems arewell known to those of skill in the art. They operate by selectivelyadsorbing the impurities from the gas. Desorption and regeneration ofthe adsorbent are accomplished by reducing the adsorptive capacity ofthe adsorbent by lowering the pressure and purging the adsorbent with aportion of the hydrogen-rich gas. Pressure swing adsorption allows morerapid sorption-desorption cycling than is possible in thermal swingadsorption.

A pressure swing cycle consists of: adsorption; depressurization; purgeat low pressure; and repressurization. This cycle may be carried outusing two or more beds of an adsorbent that are capable of selectivelyadsorbing impurities, such as methane, from a hydrogen-rich gas. Suchadsorbents include molecular sieves, particularly zeolitic molecularsieves, silica gel, activated carbon, and mixtures thereof. The mostefficient systems operate with more than two beds with one or more ofthe beds undergoing regeneration while the others are adsorbing. Thehydrogen-rich gas is used as much as possible to purge and repressureother beds.

The purified hydrogen gas product, i.e., the hydrogen-rich stream, istaken from the pressure swing adsorption. As indicated above, thehydrogen content of this hydrogen-rich stream preferably is at leastabout 90% by volume, more preferably at least 95% by volume, and evenmore preferably at least 99% by volume. As indicated above, the hydrogencontent of the feed gas to the pressure swing adsorption will be greaterthan about 40% by volume for the unit to operate effectively. At lowerhydrogen concentrations, there is insufficient product hydrogen toregenerate the pressure swing adsorption beds. According to theprocesses of the present invention, a hydrogen-rich stream may beisolated from an initial gas stream comprising a low concentration ofhydrogen (i.e., a hydrogen-depleted stream) by employing methods toraise the hydrogen content of the gas feed prior to pressure swingadsorption, as described above.

The hydrogen-rich product stream will typically be at substantially thesame pressure as the gas entering the system, since there is usuallyvery little pressure drop for the hydrogen through the pressure swingadsorption system for the hydrogen. The impurities leave the system byan “other gas” line. The impurities will typically exit the system atpressures ranging between atmospheric pressure and about 150 psig. Thepressure of the removed gases is typically an important operatingparameter of pressure swing adsorption systems. As a general rule, thelower this pressure, the higher the hydrogen recovery from the feed gas.Typically, the ratio of feed gas pressure to removed gas pressure willbe maintained at about 4:1 or higher.

Hydrocarbon Synthesis Processes

Preferably, the hydrogen-depleted stream for use in the processes of thepresent invention is isolated from a hydrocarbon synthesis process.

A hydrocarbon synthesis process refers to a series of process steps forthe conversion of a hydrocarbon source, such as natural gas, heavy oil,and coal, into more valuable hydrocarbons. The hydrocarbon synthesisprocess first comprises converting the hydrocarbon source into synthesisgas or syngas. The synthesis gas is then converted into more valuablehydrocarbons by a hydrocarbon synthesis reaction. The hydrocarbonsynthesis process may comprise one or more upgrading steps to upgradethe hydrocarbons into one or more salable hydrocarbonaceous products.Hydrocarbon synthesis processes may be used to produce a wide range ofproducts, including combustible liquid fuels, methanol, acetic acid,dimethyl ether, oxo alcohols, and isocyanates. Hydrocarbon synthesisprocesses include Fischer Tropsch processes, methanol synthesisprocesses, and the like.

The hydrocarbon synthesis reaction is the reaction for convertingsynthesis gas into higher hydrocarbons. Hydrocarbon synthesis reactionsinclude Fischer Tropsch synthesis reactions, methanol synthesisreactions, and the like.

Methanol synthesis reactions and methanol synthesis processes are wellknown to those of skill in the art. In a methanol synthesis process,syngas is derived from a hydrocarbon source. The syngas is thenconverted to methanol by contact with a catalyst under reactiveconditions. Reaction conditions and catalysts for performing methanolsynthesis reactions are well known to those of skill in the art.Methanol synthesis reactions are disclosed in, for example, U.S. Pat.Nos. 4,348,486 and 6,258,860, the contents of which are incorporated byreference in their entirety.

Fischer Tropsch synthesis reactions and Fischer Tropsch processes arealso well known to those of skill in the art. In a Fischer Tropschprocess, a hydrocarbon source, preferably natural gas, is converted intosynthesis gas. In the Fischer Tropsch synthesis reaction, highlyparaffinic higher hydrocarbon products are synthesized from thesynthesis gas. In the Fischer Tropsch synthesis reaction, synthesis gasis converted to hydrocarbons by contact with a Fischer Tropsch catalystunder reactive conditions. The products from the Fischer Tropschsynthesis reaction may range from C₁ to C₂₀₀₊ with a majority in theC₅-C₁₀₀₊ range. The Fischer Tropsch synthesis reaction can be conductedin a variety of reactor types including, for example, fixed bed reactorscontaining one or more catalyst beds, slurry reactors, fluidized bedreactors, or a combination of different type reactors. The FischerTropsch process may further comprise one or more upgrading steps toupgrade the highly paraffinic hydrocarbons into one or more salablehydrocarbonaceous products.

Preferably, the hydrocarbon synthesis reactions and processes of thepresent invention are Fischer Tropsch synthesis reactions and FischerTropsch processes.

In these hydrocarbon synthesis processes, hydrogen-depleted streams areproduced. The hydrogen-depleted streams, for use in the processes of thepresent invention, may be isolated from one or more of the process stepsin a hydrocarbon synthesis process. Combined streams, isolated from oneor more of the process steps in a hydrocarbon synthesis process, canprovide a low value, hydrogen-depleted stream. Preferably, thehydrogen-depleted stream is isolated from a source selected from thegroup consisting of (i) a tail gas from a hydrocarbon synthesis reactionunit; (ii) the syngas prior to performing the hydrocarbon synthesisreaction; (iii) a tail gas from an upgrading process; and (iv)combinations thereof. Preferably, at least a portion of thehydrogen-depleted stream is isolated from the tail gas from ahydrocarbon synthesis reaction unit.

The hydrogen-rich stream isolated according to the processes of thepresent invention may be used for a process selected from the groupconsisting of (i) upgrading a hydrocarbon product stream from thehydrocarbon synthesis process; (ii) hydrotreating a natural gas stream;(iii) recycling the hydrogen-rich stream to a hydrocarbon synthesisreaction unit; (iv) hydrogen production for uses outside the hydrocarbonsynthesis process; (v) rejuvenating a hydrocarbon synthesis reactioncatalyst; and (vi) combinations thereof.

Preferably, the processes of the present invention are used to isolatehydrogen-rich streams from streams produced in hydrocarbon synthesisprocesses, and the hydrogen-rich streams thus isolated are used in thehydrocarbon synthesis processes, thus providing an integrated process.Advantageously, in these integrated processes the hydrogen-rich streamsisolated according to the processes of the present invention may be usedfor a process selected from the group consisting of (i) upgrading ahydrocarbon product stream from the hydrocarbon synthesis process; (ii)hydrotreating a natural gas stream; (iii) recycling the hydrogen-richstream to a hydrocarbon synthesis reaction unit; (iv) rejuvenating ahydrocarbon synthesis reaction catalyst; and (v) combinations thereof.

Using the hydrogen-rich streams isolated from the hydrocarbon synthesisprocess in an integrated manner reduces or potentially eliminateshydrogen gas needed from conventional sources. Accordingly, thisintegrated process is efficient, as well as provides economicadvantages.

Fischer Tropsch Process

Preferably, the hydrocarbon synthesis process of the present inventionis a Fischer Tropsch process.

In a Fischer Tropsch process, a hydrocarbon source, preferably naturalgas, is converted into synthesis gas. The synthesis gas is convertedinto highly paraffinic higher hydrocarbon products by a Fischer Tropschsynthesis reaction. The Fischer Tropsch process may further comprise oneor more upgrading steps to upgrade the highly paraffinic hydrocarbonsinto one or more salable hydrocarbonaceous products.

In a Fischer Tropsch synthesis reaction, syngas is converted to liquidhydrocarbons by contact with a Fischer Tropsch catalyst under reactiveconditions. Typically, methane and optionally heavier hydrocarbons(ethane and heavier, coke, or coal) can be sent through a conventionalsyngas generator to provide synthesis gas. Generally, synthesis gascontains hydrogen, carbon monoxide, carbon dioxide, and water. Ifnatural gas is the feedstock and the natural gas contains sulfur, thesulfur must be removed from the natural gas because sulfur is a poisonto both reforming catalysts and Fischer Tropsch catalysts. Hydrogen isrequired to remove the sulfur from the natural gas by converting theorganic sulfur compounds into H₂S.

The presence of nitrogen, halogen, selenium, phosphorus and arseniccontaminants in the syngas is also undesirable. Means for removing thesecontaminants are well known to those of skill in the art.

If coal or coke is the feedsock, sulfur must also be removed and thesulfur removal is accomplished downstream of the syngas generation unit.Bulk removal of the sulfur is accomplished with solvent absorptionprocesses such as Selexol. ZnO guardbeds are preferred for removingtrace quantities of sulfur impurities. Means for removing othercontaminants are well known to those of skill in the art.

In the Fischer Tropsch synthesis reaction, contacting a synthesis gas,comprising a mixture of H₂ and CO, with a Fischer Tropsch catalyst undersuitable temperature and pressure reactive conditions forms liquid andgaseous hydrocarbons. The Fischer Tropsch synthesis reaction istypically conducted at temperatures of about 300-700° F. (149-371° C.),preferably about 400-550° F. (204-228° C.); pressures of about 10-600psia, (0.7-41 bars), preferably about 30-300 psia, (2-21 bars); andcatalyst space velocities of about 100-10,000 cc/g/hr, preferably about300-3,000 cc/g/hr. Examples of conditions for performing Fischer Tropschsynthesis reactions are well known to those of skill in the art.

The products of the Fischer Tropsch synthesis reaction may range from C₁to C₂₀₀₊ with a majority in the C₅ to C₁₀₀₊ range. The synthesisreaction can be conducted in a variety of reactor types or synthesisreaction units, such as fixed bed reactors containing one or morecatalyst beds, slurry reactors, fluidized bed reactors, or a combinationof different type reactors. Such synthesis reactions and reactors arewell known and documented in the literature.

The slurry Fischer Tropsch synthesis reaction, which is preferred in thepractice of the invention, utilizes superior heat (and mass) transfercharacteristics for the strongly exothermic synthesis reaction and isable to produce relatively high molecular weight, paraffinichydrocarbons when using a cobalt catalyst. In the slurry synthesisreaction, a syngas comprising a mixture of hydrogen and carbon monoxideis bubbled up as a third phase through a slurry which comprises aparticulate Fischer Tropsch type hydrocarbon synthesis catalystdispersed and suspended in a slurry liquid comprising hydrocarbonproducts of the synthesis reaction which are liquid under the reactionconditions. The mole ratio of the hydrogen to the carbon monoxide maybroadly range from about 0.5 to about 4, but is more typically withinthe range of from about 0.7 to about 2.75 and preferably from about 0.7to about 2.5. A particularly preferred Fischer Tropsch synthesisreaction is taught in EP0609079, also completely incorporated herein byreference for all purposes.

In general, Fischer Tropsch catalysts contain a Group VIII transitionmetal on a metal oxide support. The catalysts may also contain a noblemetal promoter(s) and/or crystalline molecular sieves. Suitable FischerTropsch catalysts comprise one or more of Fe, Ni, Co, Ru and Re, withcobalt being preferred. A preferred Fischer Tropsch catalyst compriseseffective amounts of cobalt and one or more of Re, Ru, Pt, Fe, Ni, Th,Zr, Hf, U, Mg and La on a suitable inorganic support material,preferably one which comprises one or more refractory metal oxides. Ingeneral, the amount of cobalt present in the catalyst is between about 1and about 50 weight percent of the total catalyst composition. Thecatalysts can also contain basic oxide promoters such as ThO₂, La₂O₃,MgO, and TiO₂, promoters such as ZrO₂, noble metals (Pt, Pd, Ru, Rh, Os,Ir), coinage metals (Cu, Ag, Au), and other transition metals such asFe, Mn, Ni, and Re. Suitable support materials include alumina, silica,magnesia and titania or mixtures thereof. Preferred supports for cobaltcontaining catalysts comprise titania. Useful catalysts and theirpreparation are known and illustrated in U.S. Pat. No. 4,568,663, whichis intended to be illustrative but non-limiting relative to catalystselection.

Certain catalysts are known to provide chain growth probabilities thatare relatively low to moderate, and the synthesis reaction productsinclude a relatively high proportion of low molecular (C₂₋₈) weightolefins and a relatively low proportion of high molecular weight (C₃₀₊)waxes. Certain other catalysts are known to provide relatively highchain growth probabilities, and the synthesis reaction products includea relatively low proportion of low molecular (C₂₋₈) weight olefins and arelatively high proportion of high molecular weight (C₃₀₊) waxes. Suchcatalysts are well known to those of skill in the art and can be readilyobtained and/or prepared.

The product from a Fischer Tropsch synthesis reaction containspredominantly paraffins. The product from a Fischer Tropsch synthesisreaction generally includes a light reaction product and a waxy reactionproduct. A tail gas is also produced. The light reaction product (i.e.,the condensate fraction) includes hydrocarbons boiling below about 700°F. (e.g., through middle distillate fuels), largely in the C₅-C₂₀ range,with decreasing amounts up to about C₃₀. The waxy reaction product(i.e., the wax fraction) includes hydrocarbons boiling above about 600°F. (e.g., vacuum gas oil through heavy paraffins), largely in the C₂₀₊range, with decreasing amounts down to C₁₀.

Both the light reaction product and the waxy product are substantiallyparaffinic. The waxy product generally comprises greater than 70 weight% normal paraffins, and often greater than 80 weight % normal paraffins.The light reaction product comprises paraffinic products with asignificant proportion of alcohols and olefins. In some cases, the lightreaction product may comprise as much as 50 weight %, and even higher,alcohols and olefins. The tail gas comprises CO, H₂, CO₂, H₂O (g), andgaseous C₁-C₅ hydrocarbons. The tail gas from the Fischer Tropschsynthesis reaction unit is a hydrogen-depleted gas stream according tothe present invention. Preferably, the tail gas from the Fischer Tropschsynthesis reactor is used in the processes of the present invention.

In the Fischer Tropsch process, the reaction products from the FischerTropsch synthesis reaction may be upgraded by one or more upgradingprocess steps. Accordingly, the Fischer Tropsch process may comprise oneor more upgrading steps to upgrade the reaction products into one ormore salable hydrocarbonaceous products. Hydrogen may be required toupgrade the products. Hydrogen may also be used to saturate olefins thatare contained in various recycle streams in the Fischer Tropsch process.

Uses for the Hydrogen-Rich Stream

The hydrogen-rich gas isolated from the processes of the presentinvention comprises greater than 90 vol. % hydrogen, preferably greaterthan 95 vol. % hydrogen, and more preferably greater than 99 vol. %hydrogen. Accordingly, the hydrogen-rich gas may be used for any purposefor which high purity hydrogen is needed.

By way of example, the hydrogen-rich gas produced from the processes ofthe present invention may be used for upgrading hydrocarbon productstreams from hydrocarbon synthesis processes. The hydrogen-rich gas maybe used for hydrotreating a natural gas stream. The hydrogen-rich gasmay used as a feed to a hydrocarbon synthesis reaction unit. As such,the hydrogen-rich gas may be recycled within the hydrocarbon synthesisprocess in which it is produced to the hydrocarbon synthesis reactionunit. The hydrogen-rich gas may be used to rejuvenate a hydrocarbonsynthesis reaction catalyst. The hydrogen-rich gas may used for hydrogenproduction for uses outside the hydrocarbon synthesis process. If thehydrogen-rich gas produced is not used within the hydrocarbon synthesisprocess, it may be appropriately shipped to other locations for use inother processes which require high purity hydrogen.

Preferably, the hydrogen-rich gas isolated according to the processes ofthe present invention is used in hydrocarbon synthesis processes fromwhich it is isolated, thus providing an integrated process. As such, thehydrogen-rich gas may be used for any purpose in the hydrocarbonsynthesis processes for which hydrogen-rich gas is needed. Preferably,the hydrogen-rich gas is used to upgrade the hydrocarbon product streamproduced in the hydrocarbon synthesis process; hydrotreat the naturalgas stream used in making the synthesis gas; recycle to the hydrocarbonsynthesis reaction unit; rejuvenate a hydrocarbon synthesis reactioncatalyst; or combinations thereof. Using the hydrogen-rich gas isolatedfrom the hydrocarbon synthesis process in the hydrocarbon synthesisprocess reduces or potentially eliminates hydrogen gas needed fromconventional sources. Accordingly, this integrated process is efficient,as well as provides economic advantages.

Rejuvenating the Hydrocarbon Synthesis Reaction Catalyst

According to the processes of the present invention, the hydrogen-richstream may be used for rejuvenation of a hydrocarbon synthesis reactioncatalyst. During the hydrocarbon synthesis reaction operation, thehydrocarbon synthesis reaction catalyst loses activity (deactivates) bydeactivating species in the syngas and deactivating species resultingfrom the synthesis reaction. These deactivating species include, forexample, nitrogen or nitrogen containing compounds. This deactivation isreversible and catalytic activity is restored (i.e., the catalyst isrejuvenated) by contacting the deactivated catalyst with hydrogen. Theactivity of a hydrocarbon synthesis reaction catalyst in a slurryreactor can be intermittently or continuously rejuvenated by contactingthe slurry with a hydrogen-rich gas to form a catalyst rejuvenatedslurry either in-situ in the hydrocarbon synthesis reactor or in anexternal rejuvenation vessel. This type of rejuvenation process isdisclosed in, for example, U.S. Pat. Nos. 5,260,239; 5,268,344; and5,283,216.

Upgrading Processes

According to the present invention hydrocarbon product streams may beupgraded by a process comprising contacting the hydrocarbon productstream with a hydrogen-rich stream, wherein the hydrogen-rich stream isisolated from a stream comprising less than 40% vol. hydrogen.

Hydrocarbon product streams isolated from hydrocarbon synthesisprocesses frequently require upgrading through hydroconversionprocesses/hydroprocessing. Fischer Tropsch products, while they arehighly paraffinic, are typically upgraded by one or more hydroconversionprocesses to provide more valuable products. Examples of hydroconversionprocesses include hydrotreating, hydrocracking, hydrogenation,hydroisomerization dewaxing, and hydrofinishing.

In addition to product streams, the initial feedstock to the syngasgenerator as well as recycle streams may require upgrading. By way ofexample, the natural gas feed to the syngas generator may requirehydrotreating to remove sulfur and sulfur containing compounds. Variousrecycle streams in the hydrocarbon synthesis process may contain olefinsthat need to be saturated by hydrotreating.

Hydroconversion processes or hydroprocessing, in general, is well knownto those of skill in the art. Among the purposes of the hydroprocessingcan be reducing, or preferably completely removing, heteroatoms such asnitrogen and sulfur. Further, hydroprocessing may reduce, or completelyremove, olefins. Moreover, hydroprocessing may increase the ratio ofiso/normal paraffins in a distillate product. Additionally,hydroprocessing may increase the production of distillate product byconverting heavy species.

Typical hydroprocessing conditions vary over a wide range and are wellknown to those of skill in the art.

Hydrotreating

Hydrotreating can be use to reduce or preferably completely removeheteroatoms, such as nitrogen and sulfur. Typical hydrotreatingconditions are well known to those of skill in the art and are describedin, by way of example, U.S. Pat. No. 6,179,995, the contents of whichare herein incorporated by reference in their entirety.

Hydrotreating conditions include a reaction temperature between 400°F.-900° F. (204° C.-482° C.), preferably 650° F.-850° F. (343° C.-454°C.); a pressure between 500 to 5000 psig (pounds per square inch gauge)(3.5-34.6 MPa), preferably 1000 to 3000 psig (7.0-20.8 MPa); a feed rate(LHSV) of 0.5 hr⁻¹ to 20 hr⁻¹ (v/v); and overall hydrogen consumption300 to 2000 scf per barrel of liquid hydrocarbon feed (53.4-356 m³ H₂/m³feed). The hydrotreating catalyst for the beds will typically be acomposite of a Group VI metal or compound thereof, and a Group VIIImetal or compound thereof supported on a porous refractory base such asalumina. Examples of hydrotreating catalysts are alumina supportedcobalt-molybdenum, nickel sulfide, nickel-tungsten, cobalt-tungsten andnickel-molybdenum. Typically such hydrotreating catalysts arepresulfided.

Hydrocracking

Hydrocracking may be conducted according to conventional methods knownto those of skill in the art. Typical hydrocracking conditions aredescribed in, by way of example, U.S. Pat. No. 6,179,995, the contentsof which are herein incorporated by reference in their entirety.Hydrocracking is used to effect a boiling range conversion of a waxyhydrocarbon feed. Typically, hydrocracking is a process of breakinglarger carbon molecules into smaller ones. It may be effected bycontacting the particular fraction or combination of fractions, withhydrogen in the presence of a suitable hydrocracking catalyst attemperatures in the range of from about 600 to 900° F. (316 to 482° C.),preferably 650 to 850° F. (343 to 454° C.), and pressures in the rangeof from about 200 to 4000 psia (13 to 272 atm), preferably 500 to 3000psia (34 to 204 atm) using space velocities based on the hydrocarbonfeedstock of about 0.1 to 10 hr⁻¹, preferably 0.25 to 5 hr⁻¹; andhydrogen consumption 500 to 2500 scf per barrel of liquid hydrocarbonfeed (89.1-445 m³ H₂/m³ feed).

The hydrocracking catalyst generally comprises a cracking component, ahydrogenation component and a binder. Such catalysts are well known inthe art. The cracking component may include an amorphous silica/aluminaphase and/or a zeolite, such as a Y-type or USY zeolite. The binder isgenerally silica or alumina. The hydrogenation component will be a GroupVI, Group VII, or Group VIII metal or oxides or sulfides thereof,preferably one or more of molybdenum, tungsten, cobalt, or nickel, orthe sulfides or oxides thereof. If present in the catalyst, thesehydrogenation components generally make up from about 5% to about 40% byweight of the catalyst. Alternatively, platinum group metals, especiallyplatinum and/or palladium, may be present as the hydrogenationcomponent, either alone or in combination with the base metalhydrogenation components molybdenum, tungsten, cobalt, or nickel. Ifpresent, the platinum group metals will generally make up from about0.1% to about 2% by weight of the catalyst.

Hydrogenation

The conditions of hydrogenation are well known in the industry andinclude temperatures above ambient and pressures greater thanatmospheric. Preferable conditions for hydrogenation include atemperature between 300 and 800° F., most preferably between 400 and600° F., a pressure between 50 and 2000 psig, most preferably between100 and 500 psig, a liquid hourly space velocity (LHSV) between 0.2 and10 hr⁻¹, most preferably between 1.0 and 3.0 hr⁻¹, and a gas ratebetween 500 and 10,000 SCFB, most preferably between 1000 and 5000 SCFB.

The catalysts used for hydrogenation are those typically used inhydrotreating, but non-sulfided catalysts containing Pt and/or Pd arepreferred, and it is preferred to disperse the Pt and/or Pd on asupport, such as alumina, silica, silica-alumina, or carbon. Thepreferred support is silica-alumina.

Hydroisomerization Dewaxing

According to the present invention, a waxy hydrocarbon feedstock can besubjected to hydroisomerization in a hydroisomerization zone.

Hydroisomerization dewaxing is intended to improve the cold flowproperties of a lubricant base oil by the selective addition ofbranching into the molecular structure. Hydroisomerization dewaxingideally will achieve high conversion levels of waxy feed to non-waxyiso-paraffins while at the same time minimizing the conversion bycracking.

Typical hydroisomerization conditions are well known to those of skillin the art and can vary widely. Hydroisomerization processes aretypically carried out at a temperature between 200° F. and 700° F.,preferably 300° F. to 650° F., with a LHSV between 0.1 and 10⁻¹,preferably between 0.25 and 5 hr⁻¹. Hydrogen is employed such that themole ratio of hydrogen to hydrocarbon is between 1:1 and 15:1. Catalystsuseful for isomerization processes are generally bifunctional catalyststhat include a dehydrogenation/hydrogenation component and an acidiccomponent. The acidic component may include one or more of amorphousoxides such as alumina, silica or silica-alumina; a zeolitic materialsuch as zeolite Y, ultrastable Y, SSZ-32, Beta zeolite, mordenite, ZSM-5and the like, or a non-zeolitic molecular sieve such as SAPO-11, SAPO-31and SZPO-41. The acidic component may further include a halogencomponent, such as fluorine. The hydrogenation component may be selectedfrom the Group VIII noble metals such as platinum and/or palladium, fromthe Group VIII non-noble metals such as nickel and tungsten, and fromthe Group VI metals such as cobalt and molybdenum. If present, theplatinum group metals will generally make up from about 0.1% to about 2%by weight of the catalyst. If present in the catalyst, the non-noblemetal hydrogenation components generally make up from about 5% to about40% by weight of the catalyst.

Hydrofinishing

The lubricant base oil products produced from the hydrocarbon synthesisprocesses may be hydrofinished in order to improve product quality andstability. During hydrofinishing, overall LHSV is about 0.25 to 2.0hr⁻¹, preferably about 0.5 to 1.0 hr⁻¹. The hydrogen partial pressure isgreater than 200 psia, preferably ranging from about 500 psia to about2000 psia. Hydrogen recirculation rates are typically greater than 50SCF/Bbl, and are preferably between 1000 and 5000 SCF/Bbl. Temperaturesrange from about 300° F. to about 750° F., preferably ranging from 450°F. to 600° F.

Suitable hydrofinishing catalysts include noble metals from Group VIIIA(according to the 1975 rules of the International Union of Pure andApplied Chemistry), such as platinum or palladium on an alumina orsiliceous matrix, and unsulfided Group VIIIA and Group VIB, such asnickel-molybdenum or nickel-tin on an alumina or siliceous matrix. U.S.Pat. No. 3,852,207 describes a suitable noble metal catalyst and mildconditions. Other suitable catalysts are described, for example, in U.S.Pat. Nos. 4,157,294, and 3,904,513. The non-noble metal (such asnickel-molybdenum and/or tungsten, and at least about 0.5, and generallyabout 1 to about 15 weight percent of nickel and/or cobalt determined asthe corresponding oxides. The noble metal (such as platinum) catalystcontains in excess of 0.01 percent metal, preferably between 0.1 and 1.0percent metal. Combinations of noble metals may also be used, such asmixtures of platinum and palladium.

Illustrative Embodiments

The illustrative embodiments are preformed with a reverse-selectivemembrane having an active-layer thickness of 1.0 micron. The membraneexhibits permeability (barrer) to various components of the initial gasfeed as summarized in Table I below.

TABLE I Gas Component Permeability (barrer) CO₂ 185 H₂ 18 CH₄ 9.2 N₂ 2.7CO 3 C₂H₆ 23 C₃H₈ 46 C₄H₁₀ 92 H₂O 1748

FIG. 1 represents one embodiment of a process for providing ahydrogen-rich stream. The process comprises performing a hydrocarbonsynthesis reaction using syngas and isolating a tail gas from thehydrocarbon synthesis reaction unit. Preferably, the hydrocarbonsynthesis reaction is a Fischer Tropsch synthesis reaction. The tail gas(1) is contacted with a reverse-selective membrane that is selectivelypermeable to CO₂ (100) providing a CO₂-enriched permeate (2) and ahydrogen-containing retentate (3). Advantageously, thehydrogen-containing retentate (3) remains at elevated pressure since itdoes not pass through the membrane and thus does not requirere-pressuring to complete the isolation process. Preferably, thehydrogen-containing retentate (3) is at a pressure of ≧ about 100 psig,and more preferably ≧ about 200 psig.

The hydrogen-containing retentate (3) is heated using heat exchanger(200). Water vapor (4) is added in excess to the hydrogen-containingretentate (3) to provide a combined stream (5). The combined stream (5)is fed into a water gas shift reactor (300). In the water gas shiftreactor (300) CO in the combined gas stream (5) reacts with water vaporin the presence of a shift catalyst at reaction conditions effective toform a mixture of hydrogen and carbon dioxide, i.e., thehydrogen-containing stream (6).

The hydrogen-containing stream (6) exits the water gas shift reactor(300) and is cooled through use of heat exchanger (200) and heatexchanger (400), with heat exchanger (400) using cooling water. Thehydrogen-containing stream (6) is then passed through a vapor-liquidseparator (500) to remove water (11) and to provide thehydrogen-containing stream (7). The hydrogen-containing stream (7) ispassed through a pressure swing adsorption unit (600) to provide ahydrogen-rich stream (10) and an absorbed gas stream (8). The absorbedgas stream (8) comprises CO, CO₂, H₂O_((g)), gaseous hydrocarbons, andresidual hydrogen and may be combined with the CO₂-enriched permeate (2)to form a combined gas stream (9) that may be burned as fuel. Thehydrogen-rich stream (10) comprises greater than 90 vol. % hydrogen,preferably greater than 95 vol. % hydrogen, and more preferably greaterthan 99 vol. % hydrogen, and may be used for any purpose for which highpurity hydrogen is needed.

Table II in FIG. 2 provides a stream summary of the gas streams fromFIG. 1. The stream summary has been generated by computer modeling.

FIG. 3 represents another embodiment of a process for providing ahydrogen-rich stream according to the present invention. The processcomprises performing a hydrocarbon synthesis reaction using syngas andisolating a tail gas from the hydrocarbon synthesis reaction unit.Preferably, the hydrocarbon synthesis reaction is a Fischer Tropschsynthesis reaction. The tail gas (21) is heated with heat exchanger(200). The tail gas (21) is then combined with water vapor (22) with thewater vapor (22) added in excess to provide a combined stream (23). Thecombined stream (23) is fed into a water gas shift reactor (300). In thewater gas shift reactor (300) CO in the combined gas stream (23) reactswith water vapor in the presence of a shift catalyst at reactionconditions effective to form a mixture of hydrogen and carbon dioxide,i.e., the hydrogen-containing stream (24).

The hydrogen-containing stream (24) exits the water gas shift reactor(300) and is cooled through use of heat exchanger (200) and heatexchanger (400), with heat exchanger (400) using cooling water. Thehydrogen-containing stream (24) is then passed through a vapor-liquidseparator (500) to remove water (31) and to provide thehydrogen-containing stream (25).

The hydrogen-containing stream (25) is contacted with areverse-selective membrane that is selectively permeable to CO₂ (100)providing a CO₂-enriched permeate (26) and a hydrogen-containingretentate (27). Advantageously, the hydrogen-containing retentate (27)remains at elevated pressure since it does not pass through the membraneand thus does not require re-pressuring to complete the isolationprocess. Preferably, the hydrogen-containing retentate (27) is at apressure of ≧ about 100 psig, and more preferably ≧ about 200 psig.

The hydrogen-containing retentate (27) is passed through a pressureswing adsorption unit (600) to provide a hydrogen-rich stream (30) andan absorbed gas stream (28). The absorbed gas stream (28) comprises CO,CO₂, H₂O_((g)), gaseous hydrocarbons, and residual hydrogen and may becombined with the CO₂-enriched permeate (26) to form a combined gasstream (29) that may be burned as fuel. The hydrogen-rich stream (30)comprises greater than 90 vol. % hydrogen, preferably greater than 95vol. % hydrogen, and more preferably greater than 99 vol. % hydrogen,and may be used for any purpose for which high purity hydrogen isneeded.

Table III in FIG. 4 provides the stream summary of the gas streams fromFIG. 3. The stream summary has been generated by computer modeling.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope thereof.

1. A process for providing a hydrogen-rich stream comprising: a)performing a hydrocarbon synthesis process using syngas; b) isolating agaseous stream comprising hydrogen from the hydrocarbon synthesisprocess, wherein the gaseous stream comprising hydrogen comprises lessthan 35 vol. % hydrogen; c) contacting the gaseous stream comprisinghydrogen with a reverse selective membrane selectively permeable to CO₂to provide a CO₂-enriched permeate and a hydrogen-containing retentate;d) passing the retentate through a water gas shift reactor to provide ahydrogen-containing stream comprising greater than 40 vol. % hydrogen;and e) passing the hydrogen-containing stream through a pressure swingadsorption unit to provide a hydrogen-rich stream comprising greaterthan 90 vol. % hydrogen.
 2. The process according to claim 1, whereinthe hydrocarbon synthesis process is a Fischer-Tropsch process.
 3. Theprocess according to claim 1, wherein the process further comprisespassing the hydrogen-containing stream through a vapor-liquid separatorto remove water.
 4. The process according to claim 1, wherein theprocess further comprises using the hydrogen-rich stream for a processselected from the group consisting of (i) upgrading a hydrocarbonproduct stream from the hydrocarbon synthesis process; (ii)hydrotreating a natural gas stream; (iii) recycling the hydrogen-richstream to a hydrocarbon synthesis reaction unit; (iv) hydrogenproduction for uses outside the hydrocarbon synthesis process; (v)rejuvenating a hydrocarbon synthesis reaction catalyst; and (vi)combinations thereof.
 5. The process according to claim 1, wherein thehydrogen-containing retentate is at a pressure of ≧ about 100 psig. 6.The process according to claim 1, wherein the hydrogen-containingretentate is at a pressure of ≧ about 200 psig.
 7. The process accordingto claim 1, wherein the hydrogen-rich stream comprising greater than 99vol. % hydrogen.
 8. The process according to claim 1, wherein thegaseous stream comprises CO₂, CO, H₂O(g), gaseous C₁-C₅ hydrocarbons,and less than 35 vol. % H₂.
 9. The process according to claim 1, whereinthe gaseous stream comprising hydrogen is isolated from a sourceselected from the group consisting of (i) a tail gas from a hydrocarbonsynthesis reaction unit; (ii) the syngas prior to performing thehydrocarbon synthesis reaction; (iii) a tail gas from an upgradingprocess; and (iv) combinations thereof.
 10. A process for providing ahydrogen-rich stream comprising: a) performing a hydrocarbon synthesisprocess using syngas; b) isolating a gaseous stream comprising hydrogenfrom the hydrocarbon synthesis process, wherein the gaseous streamcomprising hydrogen comprises less than 35 vol. % hydrogen; c) passingthe gaseous stream comprising hydrogen through a water gas shift reactorto provide a hydrogen-containing stream comprising greater than 40 vol.% hydrogen; d) contacting the hydrogen-containing stream with areverse-selective membrane selectively permeable to CO₂ to provide aCO₂-enriched permeate and a hydrogen-containing retentate; and e)passing the hydrogen-containing retentate through a pressure swingadsorption unit to provide a hydrogen-rich stream comprising greaterthan 90 vol. % hydrogen.
 11. The process according to claim 10, whereinthe hydrocarbon synthesis process is a Fischer-Tropsch process.
 12. Theprocess according to claim 10, wherein the process further comprisespassing the hydrogen-containing stream through a vapor-liquid separatorto remove water.
 13. The process according to claim 10, wherein theprocess further comprises using the hydrogen-rich stream for a processselected from the group consisting of (i) upgrading a hydrocarbonproduct stream from the hydrocarbon synthesis process; (ii)hydrotreating a natural gas stream; (iii) recycling the hydrogen-richstream to a hydrocarbon synthesis reaction unit; (iv) hydrogenproduction for uses outside the hydrocarbon synthesis process; (v)rejuvenating a hydrocarbon synthesis reaction catalyst; and (vi)combinations thereof.
 14. The process according to claim 10, wherein thehydrogen-containing retentate is at a pressure of ≧ about 100 psig. 15.The process according to claim 12, wherein the hydrogen-containingretentate is at a pressure of ≧ about 200 psig.
 16. The processaccording to claim 10, wherein the hydrogen-rich stream comprisinggreater than 99 vol. % hydrogen.
 17. The process according to claim 10,wherein the gaseous stream comprises CO₂, CO, H₂O(g), gaseous C₁-C₅hydrocarbons, and less than 35 vol. % H₂.
 18. The process according toclaim 10, wherein the gaseous stream comprising hydrogen is isolatedfrom a source selected from the group consisting of (i) a tail gas froma hydrocarbon synthesis reaction unit; (ii) the syngas prior toperforming the hydrocarbon synthesis reaction; (iii) a tail gas from anupgrading process; and (iv) combinations thereof.
 19. A process forproviding a hydrogen-rich stream comprising: a) performing a hydrocarbonsynthesis process; b) isolating a hydrogen-depleted stream comprisingless than 35 vol. % hydrogen from the hydrocarbon synthesis process; andc) isolating a hydrogen-rich stream comprising greater than 90 vol. %hydrogen from the hydrogen-depleted stream by a process comprisingcontacting the hydrogen-depleted stream with a reverse-selectivemembrane selectively permeable to CO₂ to provide a hydrogen-containingretentate and a CO₂-enriched permeate and passing thehydrogen-containing retentate through a water gas shift reactor andthrough a pressure swing adsorption unit or performing a water gas shiftreaction on the hydrogen-depleted stream to provide a treated stream andcontacting the treated stream with a reverse-selective membraneselectively permeable to CO₂ to provide a hydrogen-containing retentateand a CO₂-enriched permeate and passing the hydrogen-containingretentate through a pressure swing adsorption unit, wherein thehydrogen-depleted stream is contacted with the reverse selectivemembrane and passed through the water gas shift reactor prior to thepressure swing adsorption unit.
 20. The process according to claim 19,wherein the hydrocarbon synthesis process is a Fischer-Tropsch process.21. The process according to claim 19, wherein the hydrogen-depletedstream is isolated from a source selected from the group consisting of(i) a tail gas from a hydrocarbon synthesis reaction unit; (ii) syngasprior to performing the hydrocarbon synthesis reaction; (iii) a tail gasfrom an upgrading process; and (iv) combinations thereof.
 22. Theprocess according to claim 19, wherein the hydrogen-rich streamcomprising greater than 99 vol. % hydrogen.
 23. A process for providinga hydrogen-rich stream comprising: a) performing a hydrocarbon synthesisprocess using syngas to provide at least one hydrocarbon stream and ahydrogen-depleted stream comprising less than 40 vol. % hydrogen; b)isolating a hydrogen-containing stream from the hydrogen-depleted streamby a process comprising contacting the hydrogen-depleted stream with areverse-selective membrane selectively permeable to CO₂ to provide ahydrogen-containing retentate and a CO₂-enriched permeate and performinga water gas shift reaction on the hydrogen-containing retentate toprovide the hydrogen-containing stream, or performing a water gas shiftreaction on the hydrogen-depleted stream to provide a treated stream andcontacting the treated stream with a reverse-selective membraneselectively permeable to CO₂ to provide the hydrogen-containing streamand a CO₂-enriched permeate, wherein the hydrogen concentration on awater-free basis of the hydrogen-containing stream is at least 5 vol. %greater than the hydrogen concentration on a water-free basis of thehydrogen-depleted stream; and c) passing the hydrogen-containing streamthrough a pressure swing adsorption unit to provide a hydrogen-richstream comprising greater than 90 vol. % hydrogen.
 24. The processaccording to claim 23, wherein the hydrogen-depleted stream is contactedwith the reverse-selective membrane prior to performing the water gasshift reaction.
 25. The process according to claim 23, wherein the watergas shift reaction is performed on the hydrogen-depleted stream prior tocontacting with a reverse-selective membrane.
 26. The process accordingto claim 23, wherein the process for isolating a hydrogen-containingstream from the hydrogen-depleted stream further comprises removingwater in a vapor-liquid separator.
 27. The process according to claim23, wherein the hydrogen-depleted stream comprises less than 35 vol. %hydrogen.
 28. The process according to claim 23, wherein thehydrogen-depleted stream is isolated from a source selected from thegroup consisting of (i) a tail gas from a hydrocarbon synthesisreaction; (ii) the syngas prior to performing the hydrocarbon synthesisreaction; (iii) a tail gas from an upgrading process; and (iv)combinations thereof.
 29. The process according to claim 23, wherein theprocess further comprises using the hydrogen-rich stream for a processselected from the group consisting of (i) upgrading a hydrocarbonproduct stream from the hydrocarbon synthesis process; (ii)hydrotreating a natural gas stream; (iii) recycling the hydrogen-richstream to a hydrocarbon synthesis reaction unit; (iv) hydrogenproduction for uses outside the hydrocarbon synthesis process; (v)rejuvenating a hydrocarbon synthesis reaction catalyst; and (vi)combinations thereof.
 30. The process according to claim 23, wherein thehydrocarbon synthesis process is a Fischer-Tropsch process.
 31. Theprocess according to claim 1, wherein CO₂-enriched permeate is burned asfuel.
 32. The process according to claim 1, wherein the pressure swingadsorption unit also provides an absorbed gas stream comprising CO, CO₂,H₂O(g), gaseous hydrocarbons, and residual hydrogen and the processfurther comprises combining the absorbed gas stream with theCO₂-enriched permeate to form a combined gas stream and burning thecombined gas stream as fuel.